This invention relates in general to semiconductor power devices and more particularly to power devices with top-side drain contact using a sinker trench.
Unlike integrated circuits (ICs) which have a lateral structure with all interconnects available on the upper die surface, many power semiconductor devices have a vertical structure with the back of the die being an active electrical connection. For example, in vertical power MOSFET structures, the source and gate connections are at the top surface of the die and the drain connection is on the back side of the die. For some applications, it is desirable to make the drain connection accessible at the top side. Sinker trench structures are used for this purpose.
In a first technique, diffusion sinkers extending from the top-side of the die down to the substrate (which forms the drain contact region of the device) are used to make the drain contact available at the top surface of the die. A drawback of this technique is that the lateral diffusion during the formation of the diffusion sinkers results in consumption of a significant amount of the silicon area.
In a second technique, metal-filled vias extending from the top-side of the die clear through to the backside of the die are used to bring the back-side contact to the top-side of the die. Although, this technique does not suffer from the loss of active area as in the diffusion sinker technique, it however requires formation of very deep vias which adds to the complexity of the manufacturing process. Further, during conduction, the current is required to travel through long stretches of the substrate before reaching the drain contact, thus resulting in higher device on resistance Ron.
Thus, an improved trench structure for making a back-side contact available at the top-side is desirable.